Interactions of Temperature and Photoperiod Determine Expression of Repeat Flowering in Strawberry

Strawberry (Fragaria x ananassa) cultivars vary greatly in the expression of remontancy, or repeat flowering. To more clearly define the roles of temperature and daylength in flowering control of strawberry, the non-remontant cultivar Honeoye, and two remontant genotypes classified as day-neutral, 'Tribute' and an elite clone of Fragaria virginiana ssp. virginiana, RH 30, were grown at 14, 17, 20, 23, 26, or 29 degrees C, under a short (9 h) or long (16 h) photoperiod. Differential flowering responses of genotypes across temperature and photoperiod treatments resulted from variation in 1) the photoperiod-insensitive permissive temperature range for flowering, 2) photoperiodic requirement if temperature exceeded the photoperiod-insensitive range, and 3) the rate of development of axillary meristems. The photoperiod-insensitive temperature range varied from 14 up to 20 degrees C for 'Honeoye', 23 degrees C for RH 30, and 26 degrees C for 'Tribute'. When temperature exceeded the photoperiod-insensitive range, 'Honeoye' and RH 30 required short days for flowering, while 'Tribute' required long days. Flowering of 'Honeoye' lagged behind 'Tribute' and RH 30 by about 84 days in treatments where flowering occurred. These results indicate that temperature and floral initiation/development rate strongly influence the expression of remontancy, and that screening genotypes for day neutrality alone is unlikely to result in the development of robustly remontant cultivars.